This invention relates to substantially ohmic, that is, low resistance contacts to semiconductor materials. More particularly, it relates to such contacts on compound semiconductor materials where good ohmic contact to p and n-type conductivity material requires different metals for each type. This occurs particularly where contact is to be made to a relatively lightly doped material.
A problem arises when it is desired to form two ohmic contacts each containing a different metal on a common surface of a semiconductor, one to p-type conductivity material and the other to n-type conductivity material. It has been found that any intermixing of the two contacting metals tends to degrade the ohmic character of one or both of the contacts.
The problem of intermixing can be solved by using metal masks to control the evaporation deposition of the metals, but this procedure has distinct limitations from the standpoint of achieving the cross-spacing and area definition now required in semiconductor device fabrication. Ordinarily, such definition is achieved using photolithography which, however, if used in the straightforward fashion, is susceptible to the intermixing of the two contact metals.
Accordingly, an object of this invention is a method of making a pair of ohmic contacts to both p and n-type conductivity material on a common surface of a semiconductor body with the close-spaced definition required by current technology.